Using seabed sensors and sea-surface reflections for structural imaging of a subsurface location in a geological formation

Abstract

The present disclosure provides a technique for marine seismic imaging that processes data acquired from two or more different seismic surveys in a combined manner to advantageous effect. The different seismic surveys may use seabed sensors at same positions on the seabed, but they may have different shot locations and may be performed at different times. In one use case, the technique may be used to image a subsurface location that is difficult to image using either survey alone. In another use case, the technique may be used to image a subsurface location under an obstruction. The technique may also be utilized to efficiently monitor a reservoir over time.

What is claimed is: 
     
       1. A method of marine seismic imaging, the method comprising:
 obtaining received signals recorded by an array of sensors in a first seismic survey in which seismic signals were generated at a first set of shot locations; 
 obtaining received signals recorded by the array of sensors in a second seismic survey in which seismic signals were generated at a second set of shot locations; 
 separating up-going and down-going wavefields for each of the first and second seismic surveys; 
 selecting a first wavefield from a first shot location in the first set to a sensor in the array; 
 selecting a second wavefield from a second shot location in the second set to the sensor, wherein the second wavefield reflects from a subsurface location, and wherein the first shot location is at a location of a sea-surface reflection of the second wavefield; 
 interchanging source and sensor definitions of the first wavefield to obtain a first virtual wavefield; 
 interchanging source and sensor definitions of the second wavefield to obtain a second virtual wavefield; and 
 processing the first and second virtual wavefields to image the subsurface location. 
 
     
     
       2. The method of  claim 1 , wherein the sensors in the array comprise seabed sensors. 
     
     
       3. The method of  claim 1 , wherein the sensors in the array comprise dual sensors that measure pressure and particle velocity. 
     
     
       4. The method of  claim 1 , wherein the processing comprises a deconvolution process. 
     
     
       5. The method of  claim 1 , wherein the processing comprises a cross-correlation process. 
     
     
       6. The method of  claim 1 , further comprising:
 storing resultant image data in a tangible, non-volatile data storage medium. 
 
     
     
       7. The method of  claim 1 , wherein an obstruction blocks one or more of the shot locations in one set of the first and second sets. 
     
     
       8. The method of  claim 7 , wherein the subsurface location is beneath the obstruction. 
     
     
       9. The method of  claim 1 , wherein the second set of shot locations has a different spacing than the first set of shot locations. 
     
     
       10. A method of manufacturing a geophysical data product, the method comprising:
 obtaining received signals recorded by an array of sensors in a first seismic survey in which seismic signals were generated at a first set of shot locations; 
 obtaining received signals recorded by the array of sensors in a second seismic survey in which seismic signals were generated at a second set of shot locations; and 
 using a computer system to process the seismic signals from the first and second sets of shot locations by:
 separating up-going and down-going wavefields for each of the first and second seismic surveys; 
 selecting a first wavefield from a first shot location in the first set to a sensor in the array; 
 selecting a second wavefield from a second shot location in the second set to the sensor, wherein the second wavefield reflects from a subsurface location, and wherein the first shot location is at a location of a sea-surface reflection of the second wavefield; 
 interchanging source and sensor definitions of the first wavefield to obtain a first virtual wavefield; 
 interchanging source and sensor definitions of the second wavefield to obtain a second virtual wavefield; 
 processing the first and second virtual wavefields to generate image data of the subsurface location; and 
 recording the image data of the subsurface location on a tangible data storage medium. 
 
 
     
     
       11. The method of manufacturing of  claim 10 , wherein the sensors in the array comprise seabed sensors. 
     
     
       12. The method of manufacturing of  claim 10 , wherein the processing comprises a deconvolution process. 
     
     
       13. The method of manufacturing of  claim 10 , wherein the processing comprises a cross-correlation process. 
     
     
       14. The method of manufacturing of  claim 10 , wherein an obstruction blocks one or more of the shot locations in the second set. 
     
     
       15. The method of manufacturing of  claim 10 , wherein the second set of shot locations has a different spacing than the first set of shot locations.